* feat(landing): show live GitHub star count on the header GitHub button
Add a small client hook (useGithubStars) that fetches stargazers_count
from the GitHub API and a formatStarCount helper that renders it in
GitHub's compact repo-header style (e.g. "37.6k"). The landing header's
GitHub button now appends a star badge (faint divider + filled star +
count) on both the desktop and mobile menu entries.
Fetched client-side on purpose: LandingHeader is shared across every
marketing page, so one client fetch covers them all without threading a
server value through each render site, and each visitor calls the API
from their own IP, sidestepping the shared-outbound-IP rate limit the
server-side github-release fetcher works around with a PAT. The result
is memoized at module scope (plus in-flight dedupe); a failed fetch
caches null and the button degrades to the plain "GitHub" label.
* fix(landing): drop the star glyph from the GitHub star badge
In the GitHub button context the number already reads as the star count,
so the icon is redundant. Keep the divider + count only.
